Wireless power transfer is a growing technology, and has application in many electronic devices and systems. In addition, even non-electronic objects can be configured with wireless power capability. For example, a wall or ceiling in a house can be equipped with a coil in order to provide power to light fixtures, consumer electronics such as a television, desktop computers, a computer monitor, and so on.
Wireless power transfer refers to the transmission of electrical energy from a power source (e.g., power transmission unit, PTU) to an electrical load (e.g., power receiving unit, PRU) without a hard-wired connection between the PTU and PRU. A common technique is called resonant inductive coupling, in which wireless transmission of electrical energy is achieved between closely spaced coils (“resonators”) that are tuned to resonate at the same frequency. A coil (transmit coil) in the PTU may be driven by a time-varying signal to generate an electromagnetic (EM) field. The magnetic field will inductively couple to a nearby coil (receiver coil) in an electronic device (PRU) such as a smartphone, a computer tablet, etc. A flow of current is induced in the receiver coil, which can then be used to charge a battery in the PRU or provide power to the PRU.
Different electrical devices, however, may require a specific resonator design to account for size, height, induced voltage range, impedance range, and so on in order to provide efficient power delivery. Other design considerations include electromagnetic interference (EMI) effects. Manufacturers may have to consider operating and safety regulations, which set limits on the effects of EMI on nearby electronic devices, specific absorption rate (SAR) for humans, and so on. These considerations tend to impose constraints on the design of the resonators in a PTU.